The territory of Bassae is located between Arcadia, Triphylia and Messenia, on the western slopes of Mt. Kotilion near the ancient city of Phigaleia. The mountain is scored with ravines (vassai), which give the place its name. In this bare, rocky landscape, 1131 metres above sea level, the people of Phigaleia founded a sanctuary in honour of Apollo. A sacred road connected the sanctuary with the city, nearly thirteen kilometres away. The sanctuary was dominated by one of the most imposing monuments of ancient Greece: the temple of Apollo Epikourios, whose cult was established in the late eighth-early seventh century BC. The god was given the surname 'epikourios', either because he was thought to have helped the Phigaleians in their struggle against Sparta in 659 BC, or because he prevented the plague from spreading during the Peloponnesian War. Apollo is also named 'vassitas' in an inscription from this site.

The history of the sanctuary at Bassae is linked to the military activities of Phigaleia and to the continuous struggle between Arcadians and Spartans. The former always sided with Messenia in its wars against Sparta. The site was occupied first in the Archaic period. The earliest temple of the sanctuary was built in the late seventh century BC and a small settlement grew up around it. It is possible that many Messenians found refuge in Bassae after fleeing their homeland following the Spartan victory of 650 BC. Many votive offerings from this period were found in the topsoil around the temple. They include terracotta vases and figurines, metal figurines of humans and animals, jewellery, the tortoise-shell sound box of a lyre and many weapons, both real (made of iron) and votive (made of bronze). The offering of weapons may indicate that in the sanctuary's early years Apollo was worshiped primarily as a war god. Traces of metalworking from the Archaic period were also discovered near the temple. Although the temple's pre-Classical building history is uncertain, it is probable that the Archaic temple was reconstructed at least once or twice between 600 and 500 BC. Several architectural pieces belonging to these phases were uncovered on the site. The surviving Classical temple by Iktinos was built in approximately 420 BC. The ancient quarries that provided the building material for the temple were located to the north and northwest of the site.

Artemis and Aphrodite were also worshiped in this area, in a separate sanctuary on the highest peak of Mt. Kotilion. Demetra, too, was worshiped here, although her sanctuary has not yet been identified. The sanctuary at the top of Mt. Kotilion was probably founded by poor Phigaleians living in Bassae. Its temples were abandoned in the third century BC, unlike the sanctuary of Apollo, which remained in use in the Hellenistic and Roman periods, as shown by the stamped tiles used for repairing the temple roof. Pausanias visited the sanctuary in the second century AD and described the monuments and their history (8, 41, 7-10), particularly that of the temple of Apollo. In subsequent centuries the sanctuary was abandoned and severely damaged by earthquakes.

Remote and difficult to approach, the site remained forgotten until it was identified by French architect J. Bocher in the eighteenth century. Since then several travellers visited Bassae. The site was explored in 1812 with the permission of Veli Pasha, the Turkish commander of the Peloponnese, by a group of foreign antiquaries who removed twenty-three slabs from the Ionic cella frieze and transported them to Zante along with other sculptures. Veli Pasha's claims on the finds were silenced in exchange for a small bribe and the frieze was bought at auction by the British Museum in 1815. British intellectual C. Muller characterized this as an act of vandalism, similar to those of Lord Elgin. However, detailed drawings made during this first excavation campaign provide useful information on the monument's condition then. Subsequently, several archaeologists investigated and studied the sanctuary's monuments. Systematic research by the Greek Archaeological Society began in 1902, under the supervision by K. Kourouniotis and with the collaboration of K. Romaios and P. Kavvadias. More fragments of the Ionic frieze, now in the National Archaeological Museum, were uncovered during this period. Research by both the Archaeological Society and the Greek Archaeological Service continued until 1979. Conservation and restoration of the temple of Apollo Epikourios has been conducted since 1965 and more systematically since 1982 by the Committee for the Conservation of the Temple of Apollo Epikourios of the Greek Ministry of Culture.